There are numerous devices for delivering medicament on the market and also patented where the medicament is arranged in a container, such as a syringe, cartridge and the like, and wherein the medicament is exposed to pressure when it is to be delivered. A very common design is a generally tubular compartment having a stopper in one end of the compartment and a delivery member attached to the opposite end of the compartment, such as e.g. a needle, a nozzle or the like member capable of delivering medicament to a patient.
In order to deliver a quantity of medicament, the stopper is exposed to pressure, i.e. pushed into the compartment by a plunger rod, which could be done manually by a finger, which is the case for simple handheld syringes, or by pressure means such as springs, which is common in automatic or semi-automatic injectors.
The plunger rods of many medicament delivery devices are threaded and cooperate with threaded nuts whereby either the plunger rod is rotated or the nut is rotated when advancing the plunger rod. For disposable medicament delivery devices this solution works very well because when the plunger rod has moved to its most forward position, the medicament container is empty and the medicament delivery device can be discarded. However, for reusable medicament delivery devices, there is a problem when using threaded plunger rods because they have to be threaded back to their original position.
This operation is not appreciated by most users, and may also lead to wrong handling of the device in that there could be an uncertainty as to how far the plunger rod should be threaded back. Further, there are a number of medicament delivery devices where the delivery mechanisms, and mechanisms associated with the delivery, do not permit a return of the plunger rod.
Further, the use of multi-chamber medicament containers is becoming more and more popular wherein the medicament in dry form is mixed with a diluent just prior the medicament delivery. This entails a further operation that may be performed in different ways. Document WO2007/115424 discloses a medicament delivery device for multi-chamber containers comprising two housing parts that are in threaded engagement. When the two housing parts are threaded together a plunger rod inside the housing parts acts on a distal stopper of the medicament container, whereby the dry medicament is mixed with the diluent. The device also discloses that a dose can be set and delivered, after which the device becomes locked in order to prevent misuse. The device can then be discarded. However the device of WO2007/115424 is neither intended for multiple doses nor for multiple containers.